This invention relates to tissue factor protein. The invention further relates to novel forms and compositions thereof, and particularly to the means and methods for production of tissue factor protein to homogeneity in therapeutically significant quantities. This invention also relates to preparation of isolated deoxyribonucleic acid (DNA) coding for the production of tissue factor protein, to methods of obtaining DNA molecules which code for tissue factor protein, to the expression of human tissue factor protein utilizing such DNA, as well as to novel compounds, including novel nucleic acids encoding tissue factor protein or fragments thereof. This invention is also directed to tissue factor protein derivatives, particularly derivatives lacking the near C-terminal hydrophobic portion of the protein, and their production by recombinant DNA techniques.
Bleeding is one of the most serious and significant manifestations of disease. It may occur from a local site or may be generalized. Primary hemostasis consists principally of two components: vasoconstriction and platelet plug formation. Platelet plug formation may be divided into several stages: adhesion of platelets to subendothelial surfaces exposed by trauma; platelet activation release reaction; platelet aggregation, which results in the sequestration of additional platelets at the site, and the binding of fibrinogen and the coagulation proteins to the platelet surface which results in thrombin formation; and, fusion which is the coalescence of fibrin and fused platelets to form a stable haemostatic plug.
Blood coagulation performs two functions; the production of thrombin which induces platelet aggregation and the formation of fibrin which renders the platelet plug stable. A number of discrete proenzymes and procofactors, referred to as “coagulation factors”, participate in the coagulation process. The process consists of several stages and ends with fibrin formation. Fibrinogen is converted to fibrin by the action of thrombin. Thrombin is formed by the proteolytic cleavage of a proenzyme, prothrombin. This proteolysis is effected by activated factor X (referred to as factor Xa) which binds to the surface of activated platelets and, in the presence of factor Va and ionic calcium, cleaves prothrombin.
Activation of factor X may occur by either of two separate pathways, the extrinsic or the intrinsic (FIG. 1). The intrinsic cascade consists of a series of reactions wherein a protein precursor is cleaved to form an active protease. At each step, the newly formed protease will catalyze the activation of the precursor protease at the subsequent step of the cascade. A deficiency of any of the proteins in the pathway blocks the activation process at that step, thereby preventing clot formation and typically gives rise to a tendency to hemorrhage. Deficiencies of factor VIII or factor IX, for example, cause the severe bleeding syndromes haemophilia A and B, respectively. In the extrinsic pathway of blood coagulation, tissue factor, also referred to as tissue thromboplastin, is released from damaged cells and activates factor X in the presence of factor VII and calcium. Although activation of factor X was originally believed to be the only reaction catalyzed by tissue factor and factor VII, it is now known that an amplification loop exists between factor X, factor VII, and factor IX (Osterud, B. and S. I. Rapaport, Proc. Natl. Acad. Sci. [USA] 74:5260–5264 [1977]; Zur, M. et al., Blood 52: 198 [1978]). Each of the serine proteases in this scheme is capable of converting by proteolysis the other two into the activated form, thereby amplifying the signal at this stage in the coagulation process (FIG. 1). It is now believed that the extrinsic pathway may in fact be the major physiological pathway of normal blood coagulation (Haemostasis 13:150–155 [1983]). Since tissue factor is not normally found in the blood, the system does not continuously clot; the trigger for coagulation would therefore be the release of tissue factor from damaged tissue.
Tissue factor is an integral membrane glycoprotein which, as discussed above, can trigger blood coagulation via the extrinsic pathway (Bach, R. et al., J. Biol. Chem. 256[16]: 8324–8331 [1981]). Tissue factor consists of a protein component (previously referred to as tissue factor apoprotein-III) and a phospholipid. Osterud, B. and Rapaport, S. I., Proc. Natl. Acad. Sci. 74, 5260–5264 (1977). The complex has been found on the membranes of monocytes and different cells of the blood vessel wall (Osterud, B., Scand. J. Haematol. 32: 337–345 [1984]). Tissue factor from various organs and species has been reported to have a relative molecular mass of 42,000 to 53,000. Human tissue thromboplastin has been described as consisting of a tissue factor protein inserted into a phospholipid bilayer in an optimal ratio of tissue factor protein:phospholipid of approximately 1:80 (Lyberg, T. and Prydz, H., Nouv. Rev. Fr. Hematol. 25(5): 291–293 [1983]). Purification of tissue factor has been reported from various tissues such as,: human brain (Guha, A. et al. Proc. Natl. Acad. Sci. 83: 299–302 [1986] and Broze, C. H. et al., J. Biol. Chem. 260[20]: 10917–10920 [1985]); bovine brain (Bach, R. et al., J. Biol. Chem. 256: 8324–8331 [1981]); human placenta (Bom, V. J. J. et al., Thrombosis Res. 42:635–643 [1986]; and, Andoh, K. et al., Thrombosis Res. 43:275–286 [1986]); ovine brain (Carlsen, E. et al., Thromb. Haemostas. 48[3], 315–319 [1982]); and, lung (Glas, P. and Astrup, T., Am. J. Physiol. 219, 1140–1146 [1970]). It has been shown that bovine and human tissue thromboplastin are identical in size and function (see Broze, G. H. et al., J. Biol. Chem. 260[20], 10917–10920 [1985]). It is widely accepted that while there are differences in structure of tissue factor protein between species there are no functional differences as measured by in vitro coagulation assays (Guha et al. supra). Furthermore, tissue factor isolated from various tissues of an animal, e.g. dog brain, lung, arteries and vein was similar in certain respects such as, extinction coefficient, content of nitrogen and phosphorous and optimum phospholipid to lipid ratio but differed slightly in molecular size, amino acid content, reactivity with antibody and plasma half life (Gonmori, H. and Takeda, Y., J. Physiol. 229[3], 618–626 [1975]). All of the tissue factors from the various dog organs showed clotting activity in the presence of lipid. Id. It is widely accepted that in order to demonstrate biological activity, tissue factor must be associated with phospholipids in vitro (Pitlick, F. A., and Nemerson, Y., Biochemistry 9: 5105–5111 [1970] and Bach, R. et al. supra. at 8324). It has been shown that the removal of the phospholipid component of tissue factor, for example by use of a phospholipase, results in a loss of its biological activity in vitro (Nemerson, Y., J. C. I. 47: 72–80 [1968]). Relipidation can restore in vitro tissue factor activity (Pitlick. F. A. and Nemerson, Y., supra and Freyssinet, J. M. et al., Thrombosis and Haemostasis 55: 112–118 [1986]). An amino terminal sequence of tissue factor (Bach, R. et al., Am. Heart Assoc. [November, 1986], Morrissey, J. H. et al., Am. Heart Assoc. [November, 1986]) and a CNBr peptide fragment (Bach, R. et al. supra) have been determined.
Infusion of tissue factor has long been believed to compromise normal haemostasis. In 1834 the French physiologist de Blainville first established that tissue factor contributed directly to blood coagulation (de Blainville, H. Gazette Medicale Paris, Series 2, 524 [1834]). de Blainville also observed that intravenous infusion of a brain tissue suspension caused immediate death which he observed was correlated with a hypercoagulative state giving rise to extensively disseminated blood clots found on autopsy. It is now well accepted that intravenous infusion of tissue thromboplastin induces intravascular coagulation and may cause death in various animals (Dogs: Lewis, J. and Szeto I. F., J. Lab. Clin. Med. 60: 261–273 [1962]; rabbits: Fedder, G. et al., Thromb. Diath. Haemorrh. 27: 365–376 [1972]; rats: Giercksky, K. E. et al., Scand. J. Haematol. 17: 305–311 [1976]; and, sheep: Carlsen, E. et al., Thromb. Haemostas. 48: 315–319 [1982]).
Although the isolation of tissue factor has been described in the literature as shown above, the precise structure of tissue factor protein has not been previously established. While some quantities of “purified” tissue factor protein have been available as obtained from various tissues, the low concentration of tissue factor protein in blood and tissues and the high cost, both economic and of effort, of purifying the protein from tissues makes this a scarce material. It is an object of the present invention to isolate DNA encoding tissue factor protein and to produce useful quantities of human tissue factor protein using recombinant techniques. It is a further object to prepare novel forms of tissue factor protein. This and other objects of this invention will be apparent from the specification as a whole.